The fermentation of carbohydrates to form butanol and acetone by Clostridium acetobutylicum (hereafter abbreviated C. acetobutylicum) was disclosed by Weizmann in U.S. Pat. No. 1,315,585. For many years, this process was used for the preparation of acetone and butanol, and a certain amount of ethyl alcohol was obtained as a by-product.
Eventually, the microbial process was displaced by chemical processes which provide the same products using cheap fossil fuel raw materials. However, the gradual depletion of petroleum fossil fuel with the resultant increase in prices of petrochemical feedstocks has revived interest in the fermentation reaction that uses carbohydrates, which are renewable raw materials.
The earlier commercial production of butanol by the fermentaion process gave relatively large amounts of the less-valuable solvent, acetone, as a by-product. In addition, large volumes of hydrogen gas were evolved. The formation of these by-products uses up carbohydrate which could be otherwise converted to the more-valuable butanol. It would, therefore, be an improvement in the process if some means could be provided to reduce the formation of the by-products, acetone and hydrogen, and to increase the yield of butanol.
In 1937, Simon and Weizmann reported an attempt to modify the fermentation by C. acetobutylicum with carbon monoxide, Enzymologia, 4. 169-188 (1937). They reported there was no change in the fermentation of a 5% suspension of corn mash when a slow stream of carbon monoxide was passed through the fermentation medium. Simon later reported, Arch. Biochem., 13, 237-243 (1947), that this failure to influence the fermentation with a 5% corn mash is apparently due to mechanical factors. When the fermentation is run with a more dilute mash or in the presence of simpler sugars, it is almost completely inhibited when a stream of carbon monoxide is passed through the medium. Simon also isolated bacterial cells from a 24-hour fermentation and found that they would ferment glucose in an atmosphere of carbon monoxide. Under these conditions, the product was exclusively racemic lactic acid.
We have now discovered, surprisingly that if carbon monoxide is diluted sufficiently it exhibits an entirely different influence on the course of the fermentation of carbohydrates by C acetobutylicum. When the fermentation is run in the presence of properly diluted carbon monoxide, the formation of acetone and hydrogen is reduced and the production of butanol is increased. Furthermore, if the fermentation is carried out in the presence of butyric acid, the carbon monoxide greatly enhances its conversion to butyl alcohol.